Synthesis and Biological Evaluation of the First Example of NO-Donor Histone Deacetylase Inhibitor

A review of progress in o-aminobenzamide-based HDAC inhibitors with dual targeting capabilities for cancer therapy

Histone deacetylases, as a new class of anticancer targets, could maintain homeostasis by catalyzing histone deacetylation and play important roles in regulating the expression of target genes. Due to the fact that simultaneous intervention with dual tumor related targets could improve treatment effects, researches on innovative design of dual-target drugs are underway. HDAC is known as a "sensitizer" for the synergistic effects with other anticancer-target drugs because of its flexible structure design. The synergistic effects of HDAC inhibitor and other target inhibitors usually show enhanced inhibitory effects on tumor cells, and also provide new strategies to overcome multidrug resistance. Many research groups have reported that simultaneously inhibiting HDAC and other targets, such as tubulin, EGFR, could enhance the therapeutic effects. The o-aminobenzamide group is often used as a ZBG group in the design of HDAC inhibitors with potent antitumor effects. Given the prolonged inhibitory effects and reduced toxic side effects of HDAC inhibitors using o-aminobenzamide as the ZBG group, the o-aminobenzamide group is expected to become a more promising alternative to hydroxamic acid. In fact, o-aminobenzamide-based dual inhibitors of HDAC with different chemical structures have been extensively prepared and reported with synergistic and enhanced anti-tumor effects. In this work, we first time reviewed the rational design, molecular docking, inhibitory activities and potential application of o-aminobenzamide-based HDAC inhibitors with dual targeting capabilities in cancer therapy, which might provide a reference for developing new and more effective anticancer drugs.

Significance of Five-Membered Heterocycles in Human Histone Deacetylase Inhibitors

Five-membered heteroaromatic rings, in particular, have gained prominence in medicinal chemistry as they offer enhanced metabolic stability, solubility and bioavailability, crucial factors in developing effective drugs. The unique physicochemical properties and biological effects of five-membered heterocycles have positioned them as key structural motifs in numerous clinically effective drugs. Hence, the exploration of five-ring heterocycles remains an important research area in medicinal chemistry, with the aim of discovering new therapeutic agents for various diseases. This review addresses the incorporation of heteroatoms such as nitrogen, oxygen and sulfur into the aromatic ring of these heterocyclic compounds, enhancing their polarity and facilitating both aromatic stacking interactions and the formation of hydrogen bonds. Histone deacetylases are present in numerous multiprotein complexes within the epigenetic machinery and play a central role in various cellular processes. They have emerged as important targets for cancer, neurodegenerative diseases and other therapeutic indications. In histone deacetylase inhibitors (HDACi's), five-ring heterocycles perform various functions as a zinc-binding group, a linker or head group, contributing to binding activity and selective recognition. This review focuses on providing an up-to-date overview of the different five-membered heterocycles utilized in HDACi motifs, highlighting their biological properties. It summarizes relevant publications from the past decade, offering insights into the recent advancements in this field of research.

NO-HDAC dual inhibitors

HDAC inhibitors and NO donors have both demonstrated independently broad therapeutic potential in a variety of diseases. Borretto et al. presented the topic of NO-HDAC dual inhibitors for the first time in 2013 as an attractive new topic. Here we collected the general structure of all synthesized NO-HDAC dual inhibitors, lead compounds, synthesis methods and biological features of the most potent dual NO-HDAC inhibitor in each category with the intention of assisting in the synthesis and optimization of new drug-like compounds for diverse diseases. Based on studies done so far, NO-HDAC dual inhibitors have displayed satisfactory results against wound healing (3), heart hypertrophy (3), inflammatory, cardiovascular, neuromuscular illnesses (11a-11e) and cancer (6a-6o, 9a-9d, 10a-10d, 16 and 17). NO-HDAC dual inhibitors can have high therapeutic potential for various diseases due to their new properties, NO properties, HDAC inhibitor properties and also due to the effects of NO on HDAC enzymes.

Comprehensive review for anticancer hybridized multitargeting HDAC inhibitors

Despite the encouraging clinical progress of chemotherapeutic agents in cancer treatment, innovation and development of new effective anticancer candidates still represents a challenging endeavor. With 15 million death every year in 2030 according to the estimates, cancer has increased rising of an alarm as a real crisis for public health and health systems worldwide. Therefore, scientist began to introduce innovative solutions to control the cancer global health problem. One of the promising strategies in this issue is the multitarget or smart hybrids having two or more pharmacophores targeting cancer. These rationalized hybrid molecules have gained great interests in cancer treatment as they are capable to simultaneously inhibit more than cancer pathway or target without drug-drug interactions and with less side effects. A prime important example of these hybrids, the HDAC hybrid inhibitors or referred as multitargeting HDAC inhibitors. The ability of HDAC inhibitors to synergistically improve the efficacy of other anti-cancer drugs and moreover, the ease of HDAC inhibitors cap group modification prompt many medicinal chemists to innovate and develop new generation of HDAC hybrid inhibitors. Notably, and during this short period, there are four HDAC inhibitor hybrids have entered different phases of clinical trials for treatment of different types of blood and solid tumors, namely; CUDC-101, CUDC-907, Tinostamustine, and Domatinostat. This review shed light on the most recent hybrids of HDACIs with one or more other cancer target pharmacophore. The designed multitarget hybrids include topoisomerase inhibitors, kinase inhibitors, nitric oxide releasers, antiandrogens, FLT3 and JAC-2 inhibitors, PDE5-inhibitors, NAMPT-inhibitors, Protease inhibitors, BRD4-inhibitors and other targets. This review may help researchers in development and discovery of new horizons in cancer treatment.

Dual inhibitors of histone deacetylases and other cancer-related targets: A pharmacological perspective

Epigenetic enzymes histone deacetylases (HDACs) are clinically validated anticancer drug targets which have been studied intensively in the past few decades. Although several drugs have been approved in this field, they are still limited to a subset of hematological malignancies (in particular T-cell lymphomas), with therapeutic potential not fully realized and the drug-resistance occurred after a certain period of use. To maximize the therapeutic potential of these classes of anticancer drugs, and to extend their application to solid tumors, numerous combination therapies containing an HDACi and an anticancer agent from other mechanisms are currently ongoing in clinical trials. Recently, dual targeting strategy comprising the HDACs component has emerged as an alternative approach for combination therapies. In this perspective, we intend to gather all HDACs-containing dual inhibitors related to cancer therapy published in literature since 2015, classify them into five categories based on targets' biological functions, and discuss the rationale why dual acting agents should work better than combinatorial therapies using two separate drugs. The article discusses the pharmacological aspects of these dual inhibitors, including in vitro biological activities, pharmacokinetic studies, in vivo efficacy studies, as well as available clinical trials. The review of the current status and advances should provide better analysis for future opportunities and challenges of this field.

Paradigm shift of "classical" HDAC inhibitors to "hybrid" HDAC inhibitors in therapeutic interventions

'Epigenetic' regulation of genes via post-translational modulation of proteins is the current mainstay approach for the disease therapies, particularly explored in the Histone Deacetylase (HDAC) class of enzymes. Mainly sight saw in cancer chemotherapeutics, HDAC inhibitors have also found a promising role in other diseases (neurodegenerative disorders, cardiovascular diseases, and viral infections) and successfully entered in various combination therapies (pre-clinical/clinical stages). The prevalent flexibility in the structural design of HDAC inhibitors makes them easily tuneable to merge with other pharmacophore modules for generating multi-targeted single hybrids as a novel tactic to overcome drawbacks of polypharmacy. Herein, we reviewed the putative role of prevalent HDAC hybrids inhibitors in the current and prospective stage as a translational approach to overcome the limitations of the existing conventional drug candidates (parent molecule) when used either alone (drug resistance, solubility issues, adverse side effects, selectivity profile) or in combination (pharmacokinetic interactions, patient compliance) for treating various diseases.

Synthesis and biological study of class I selective HDAC inhibitors with NO releasing activity

Based on the multi-mechanism antitumor strategy and the regulatory effect of nitric oxide (NO) on histone deacetylases (HDACs), a series of N-acyl-o-phenylenediamine-based HDAC inhibitors equipped with the phenylsulfonylfuroxan module as NO donor was designed, synthesized and biologically evaluated. The in vitro HDAC inhibitory assays revealed that compared with the clinical class I selective HDAC inhibitor MS275, compounds 7c, 7d and 7e possessed similar HDAC inhibitory potency and selective profile, which were confirmed by the results of western blot analysis. The western blot analysis also showed that NO scavenger N-acetyl cysteine (NAC) could weaken the intracellular HDAC inhibitory ability of compound 7c, supporting the HDAC inhibitory effect of NO generated by 7c. It is worth noting that compounds 7c, 7d and 7e exhibited more potent in vitro antiproliferative activities than MS275 against all four tested solid tumor cell lines. The promising in vivo antitumor potency of 7c was demonstrated in a HCT116 xenograft model.

Synthesis and Antiproliferative Activity of Nitric Oxide-Donor Largazole Prodrugs

The marine natural product Largazole is the most potent Class I HDAC inhibitor identified to date. Since its discovery, many research groups have been attracted by the structural complexity and the peculiar anticancer activity, due to its capability to discriminate between tumor cells and normal cells. Herein, we discuss the synthesis and the in vitro biological profile of hybrid analogues of Largazole, as dual HDAC inhibitor and nitric oxide (NO) donors, potentially useful as anticancer agents. In particular, the metabolic stability of the modified thioester moiety of Largazole, bearing the NO-donor function/s, the in vitro release of NO, and the antiproliferative activity in tumor cell lines are presented.

Synthesis and biological evaluation of novel benzofuroxan-based pyrrolidine hydroxamates as matrix metalloproteinase inhibitors with nitric oxide releasing activity

On the basis of the strategy of "multifunctional drugs", a series of novel matrix metalloproteinase inhibitors (MMPIs) containing benzofuroxan scaffold as a nitric oxide donor were designed, synthesized and evaluated. All synthesized compounds, especially 16a, exhibited potent MMP-2,9 inhibitory activities, anti-proliferative activities and could produce high levels of NO in Hela cells. They were also evaluated for both of their anti-invasion and anti-angiogenesis effects. Furthermore, compared with LY52, 16a demonstrated competitive antitumor activity in vivo. These hybrid NO-MMPIs might offer suitable scaffolds to develop valuable MMP inhibitors for the further discovery of novel anti-cancer drugs.

Epigenetic polypharmacology: from combination therapy to multitargeted drugs

The modern drug discovery process has largely focused its attention in the so-called magic bullets, single chemical entities that exhibit high selectivity and potency for a particular target. This approach was based on the assumption that the deregulation of a protein was causally linked to a disease state, and the pharmacological intervention through inhibition of the deregulated target was able to restore normal cell function. However, the use of cocktails or multicomponent drugs to address several targets simultaneously is also popular to treat multifactorial diseases such as cancer and neurological disorders. We review the state of the art with such combinations that have an epigenetic target as one of their mechanisms of action. Epigenetic drug discovery is a rapidly advancing field, and drugs targeting epigenetic enzymes are in the clinic for the treatment of hematological cancers. Approved and experimental epigenetic drugs are undergoing clinical trials in combination with other therapeutic agents via fused or linked pharmacophores in order to benefit from synergistic effects of polypharmacology. In addition, ligands are being discovered which, as single chemical entities, are able to modulate multiple epigenetic targets simultaneously (multitarget epigenetic drugs). These multiple ligands should in principle have a lower risk of drug-drug interactions and drug resistance compared to cocktails or multicomponent drugs. This new generation may rival the so-called magic bullets in the treatment of diseases that arise as a consequence of the deregulation of multiple signaling pathways provided the challenge of optimization of the activities shown by the pharmacophores with the different targets is addressed.

Nitric oxide, the new architect of epigenetic landscapes

Nitric oxide (NO) is an endogenously produced signaling molecule with multiple regulatory functions in physiology and disease. The most studied molecular mechanisms underlying the biological functions of NO include its reaction with heme proteins and regulation of protein activity via modification of thiol residues. A significant number of transcriptional responses and phenotypes observed in NO microenvironments, however, still lack mechanistic understanding. Recent studies shed new light on NO signaling by revealing its influence on epigenetic changes within the cell. Epigenetic alterations are important determinants of transcriptional responses and cell phenotypes, which can relay heritable information during cell division. As transcription across the genome is highly sensitive to these upstream epigenetic changes, this mode of NO signaling provides an alternate explanation for NO-mediated gene expression changes and phenotypes. This review will provide an overview of the interplay between NO and epigenetics as well as emphasize the unprecedented importance of these pathways to explain phenotypic effects associated with biological NO synthesis.

Inside HDACs with more selective HDAC inhibitors

Inhibitors of histone deacetylases (HDACs) are nowadays part of the therapeutic arsenal mainly against cancers, with four compounds approved by the Food and Drug Administration. During the last five years, several groups have made continuous efforts to improve this class of compounds, designing more selective compounds or compounds with multiple capacities. After a survey of the HDAC biology and structures, this review summarizes the results of the chemists working in this field, and highlights when possible the behavior of the molecules inside their targets.

Multitarget Drugs: an Epigenetic Epiphany

Epigenetics refers to changes in a biological phenotype that are not due to an underlying change in genotype. In eukaryotes, epigenetics involves a set of chemical modifications of the DNA and the histone proteins in nucleosomes. These dynamic changes are carried out by enzymes and modulate protein-protein and protein-nucleic acid interactions to determine whether specific genes are expressed or silenced. Both the epigenetic enzymes and recognition domains are currently important drug discovery targets, particularly for the treatment of cancer. This review summarizes the progress of epigenetic targets that have reached a clinical stage: DNA methyltransferases, histone deacetylases, lysine methyltransferases, lysine demethylases, and bromodomains; this is followed by a comprehensive survey of multitarget drugs that have included an epigenetic target as one of their mechanisms of action.

Design of hybrid heterocyclic systems with a furoxanylpyridine core via tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans

Synthetic strategy for the synthesis of hybrid heterocyclic systems with the furoxanylpyridine core based on the tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans with enamine and norbornadiene has been developed.

Design, synthesis, and antitumor evaluation of novel histone deacetylase inhibitors equipped with a phenylsulfonylfuroxan module as a nitric oxide donor

On the basis of the strategy of creating multifunctional drugs, a novel series of phenylsulfonylfuroxan-based hydroxamates with histone deacetylase (HDAC) inhibitory and nitric oxide (NO) donating activities were designed, synthesized, and evaluated. The most potent NO donor-HDAC inhibitor (HDACI) hybrid, 5c, exhibited a much greater in vitro antiproliferative activity against the human erythroleukemia (HEL) cell line than that of the approved drug SAHA (Vorinostat), and its antiproliferative activity was diminished by the NO scavenger hemoglobin in a dose-dependent manner. Further mechanism studies revealed that 5c strongly induced cellular apoptosis and G1 phase arrest in HEL cells. Animal experiment identified 5c as an orally active agent with potent antitumor activity in a HEL cell xenograft model. Interestingly, although compound 5c was remarkably HDAC6-selective at the molecular level, it exhibited pan-HDAC inhibition in a western blot assay, which is likely due to class I HDACs inhibition caused by NO release at the cellular level.

Efficient assembly of mono- and bis(1,2,4-oxadiazol-3-yl)furoxan scaffolds via tandem reactions of furoxanylamidoximes

Tandem protocols for the synthesis of new types of hybrid molecules – (1,2,4-oxadiazol-3-yl)furoxans based on the furoxanylamidoximes heterocyclization have been developed.